Bug 2521462 (CVE-2026-74659)

Summary: CVE-2026-74659 kernel: net: bridge: mrp: fix uninitialised bytes on the wire
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: ---
Doc Text:
A flaw was found in the Linux kernel's Multiple Registration Protocol (MRP) bridge module. When constructing MRP test frames, the br_mrp_alloc_test_skb() function fails to properly initialize certain fields. This oversight results in three uninitialized bytes being transmitted in every MRA MRP_Test frame, potentially leading to the disclosure of sensitive information.
 Story Points: ---
Clone Of: Environment:
Last Closed: Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-08-22 15:46:46 UTC 
In the Linux kernel, the following vulnerability has been resolved:

net: bridge: mrp: fix uninitialised bytes on the wire

br_mrp_alloc_test_skb() builds MRP test frames on an skb from
dev_alloc_skb(), which does not clear the linear data area.  On the MRA
ring-role branch the sub-option TLV header is appended with

	sub_tlv = skb_put(skb, sizeof(*sub_tlv));
	sub_tlv->type = BR_MRP_SUB_TLV_HEADER_TEST_AUTO_MGR;

so sub_tlv->length is never written, and the two trailing alignment bytes
are appended with a bare skb_put() that does not clear them either.  The
neighbouring oui and sub_opt regions are explicitly zeroed, so three
uninitialised bytes are left in every MRA MRP_Test frame that goes out.

Put the sub-option TLV header and the alignment padding in a single
skb_put_zero(), which clears both.  The AUTO_MGR sub-TLV carries no
payload, so the zeroed length field is already the value it should have.
Comment 1 Keith Grant 2026-08-24 15:50:31 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026082227-CVE-2026-74659-16e5@gregkh/T